A cup of this kind is prior art in Japanese published patent application JP2001-192015A. The bottom skirt of the known cup widens out downwards. The widening serves to fix an outer sleeve, which surrounds the interior defining sleeve by forming a hollow space. As the widening of the bottom skirt defines the distance between the inner sleeve and the outer sleeve, the widening of the bottom skirt along the periphery must be continuous. The outer sleeve is placed around the bottom skirt, folded inwards and attached thereto. When the outer sleeve is being attached to the bottom skirt, it may occur that the liquid tightness of the bottom skirt is affected. The attaching of the outer sleeve by means of folding inwards is a very complicated process.
In the case of the known cup, the outer sleeve surrounds the bottom skirt completely, so that this can no longer be seen from the outside. When the outer sleeve is folded inwards and attached from the inside to the bottom skirt, counter-holding from the outside is no longer possible. The outer sleeve can only be pressed against from the inside with a very low level of force, which the bottom skirt can take up itself. If the pressure force is too great, the bottom skirt may tear; on the other hand, the attaching of the outer sleeve can be inadequate if the pressure force is too low. In the case of attaching the outer sleeve by means of heat sealing it can occur that the sealing between the bottom and the sleeve defining the interior dissolves, as when the inwardly folded outer sleeve is being sealed, no counter pressure can be exerted from the outside on the bottom skirt.
In the case of cups made of paper material, the bottom skirt is a very important element of the cup. The bottom skirt is necessary for the connection between the sleeve and the bottom. At least two material layers are disposed in thickness direction on top of one another, namely the material of the bottom and the material of the interior-defining sleeve. The bottom is advantageously pot-shaped, whose open side faces away from the filling opening of the cup. The at least two material layers are advantageously arranged along the wall of the pot-shaped bottom. It can be additionally provided that for example the sleeve is folded inwards around the material of the bottom, and that the bottom skirt consists of three or more material layers. The material of the bottom is glued or sealed to the material of the sleeve in the area of the bottom skirt, in order that it is liquid-tight for at least a certain time.
The term “paper material”, from which the bottom and the sleeve are made, includes various materials, which comprise at least one layer of paper, paperboard or cardboard. In addition the material can comprise one or more layers made of synthetics and/or aluminium. It can also be provided that the paper material is waxed or coated, in order to provide a resistance against the liquid with which the cup is subsequently filled. The paper material is advantageously coated at least on the side facing the interior with a thin synthetic layer, preferably made of polyethylene. In contrast to purely synthetic material, the formability and in particular the degree to which such paper material is ductile is limited. In the case of too great a deformation, the paper material itself, or a provided coating, may tear, so that the liquid-tight properties are impaired. The bottom skirt is therefore an essential design feature in the case of cups made of paper material and cannot be omitted.